Stainless Steel Coil Tube for Air-Cooled Heat Pump Shell-and-Coil Heat Exchanger (GSN Series)
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered spiral tube component specifically designed for integration into air-cooled heat pump shell-and-coil heat exchangers of the GSN series. This product represents a critical heat transfer element within the heat pump system, where refrigerant flows through the coiled tube while ambient air passes over the external surface, enabling efficient thermal exchange. The coil tube geometry maximizes the heat transfer surface area within a compact shell enclosure, making it ideal for both heating and cooling cycles in commercial and industrial heat pump applications.
This product is classified under the literature study category and is derived from technical research and development focused on the GSN-type shell-and-coil heat exchanger system. The design philosophy emphasizes high thermal efficiency, corrosion resistance, and long-term operational reliability in demanding environmental conditions.
Material & Properties
Base Material
- Material Grade: Austenitic stainless steel conforming to ASTM A269 / ASTM A213 standards
- Common Grades Available: SUS304 (UNS S30400), SUS316 (UNS S31600), SUS321 (UNS S32100)
- Equivalent Standards: EN 10216-5, GB/T 12771, JIS G3459
Mechanical Properties
- Tensile Strength: ≥ 520 MPa (75,000 psi) minimum for Grade 304
- Yield Strength: ≥ 205 MPa (29,750 psi) minimum
- Elongation: ≥ 40% in 50 mm gauge length
- Hardness: ≤ 22 HRB (annealed condition)
- Impact Strength: Excellent at both ambient and cryogenic temperatures
Thermal & Corrosion Resistance
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (Grade 304)
- Operating Temperature Range: -196°C to +870°C (Grade 304); -196°C to +870°C (Grade 316)
- Corrosion Resistance: Superior resistance to atmospheric corrosion, chlorides (Grade 316), and intergranular corrosion
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm, 9.52 mm, 12.7 mm, 15.88 mm, 19.05 mm | ±0.1 mm |
| Wall Thickness | 0.8 mm – 1.5 mm | ±0.05 mm |
| Coil Diameter | 100 mm – 500 mm (configurable) | ±2 mm |
| Coil Pitch (Spacing) | 5 mm – 25 mm (adjustable per design) | ±0.5 mm |
| Tube Length (Uncoiled) | 5 m – 50 m (custom lengths available) | ±10 mm |
| Surface Finish | Mill finish, polished (Ra ≤ 0.8 μm), or electropolished (Ra ≤ 0.4 μm) | Per customer specification |
| End Treatment | Plain cut, beveled, threaded, or flanged | Per drawing |
| Refrigerant Pressure Rating | Up to 4.0 MPa (580 psi) working pressure | Hydrostatic test at 6.0 MPa |
| Heat Transfer Efficiency | Overall heat transfer coefficient: 800 – 1,200 W/(m²·K) | — |
| Standard Reference | GB/T 12771, ASTM A269, EN 10216-5 | — |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and optimal thermal performance:
- Material Selection & Inspection: Cold-rolled stainless steel strip is sourced from certified mills and subjected to spectroscopic analysis to verify chemical composition (C ≤ 0.08%, Ni ≥ 8.0%, Cr ≥ 18.0% for Grade 304).
- Coil Forming (Spiral Winding): The flat strip is wound around a precision mandrel using CNC-controlled coil forming equipment to achieve uniform pitch and diameter. The forming process is performed at controlled temperatures to prevent work hardening and maintain ductility.
- Welding & Seam Sealing: Longitudinal and helical welds are performed using Tungsten Inert Gas (TIG) welding or orbital welding techniques with argon shielding to ensure leak-tight joints. Weld bead geometry is controlled to minimize flow resistance and turbulence.
- Heat Treatment (Solution Annealing): Post-weld annealing at 1050°C – 1150°C followed by water quenching to relieve residual stresses, restore full solution-annealed microstructure, and maximize corrosion resistance.
- Precision Machining & Dimensional Verification: End preparation, straightening of inlet/outlet legs, and dimensional inspection using Coordinate Measuring Machine (CMM) and laser measurement systems.
- Surface Treatment: Optional pickling, passivation, or electropolishing to achieve the required surface finish and enhance corrosion resistance.
- Pressure Testing & Leak Detection: Hydrostatic pressure testing at 1.5× the maximum working pressure, followed by helium leak detection at sensitivity of 1×10⁻⁹ Pa·m³/s.
Applications
Primary Applications
- Air-Cooled Heat Pump Systems: The coil tube serves as the refrigerant-side heat transfer element in GSN-type shell-and-coil heat exchangers used in commercial air-to-water heat pumps for space heating and cooling.
- Industrial Process Heating & Cooling: Integration into process heat recovery systems where high-efficiency heat exchange is required in corrosive environments.
- Refrigeration Systems: Condenser and evaporator applications in commercial refrigeration units operating with HFC, HFO, and ammonia refrigerants.
- Geothermal Heat Pump Systems: Ground-loop heat exchangers where the coil tube transfers thermal energy between ground water and refrigerant.
Secondary Applications
- Food and pharmaceutical processing equipment requiring sanitary-grade heat transfer components
- Marine and offshore cooling systems demanding high corrosion resistance
- Automotive thermal management systems
- Solar thermal collector loop heat exchangers
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and holds the following certifications and compliances:
- ISO 9001:2015 – Quality Management System certification for manufacturing operations
- ISO 14001:2015 – Environmental Management System certification
- ASME Stamp (U Stamp) – Authorization for pressure-containing components
- EN 10204 3.1 Certificate – Third-party material inspection and testing documentation
- CE Marking – Compliance with European Pressure Equipment Directive (PED 2014/68/EU)
- GB/T Standards Compliance – Full conformance with Chinese national standards for stainless steel seamless and welded tubes
- Material Traceability: Each coil tube batch is accompanied by a Mill Test Certificate (MTC) documenting chemical composition, mechanical properties, heat treatment records, and non-destructive testing (NDT) results
- Non-Destructive Testing (NDT):strong> 100% visual inspection, dye penetrant testing (DPT) on welds, and radiographic testing (RT) on random samples per ASTM E165 and ASTM E94
Unique Selling Points
1. Optimized Coil Geometry for Maximum Heat Transfer: The precise pitch control and uniform coil diameter achieved through CNC mandrel winding ensure consistent airflow distribution and maximize the heat transfer surface-to-volume ratio, resulting in superior thermal performance compared to conventional straight-tube designs.
2. Superior Corrosion Resistance in Harsh Environments: The use of high-purity austenitic stainless steel (Grade 304/316) provides exceptional resistance to atmospheric corrosion, de-icing salt exposure, and chemical attack from various refrigerants, ensuring a service life exceeding 20 years without degradation of thermal efficiency.
3. Leak-Tight Orbital Welding Technology: Advanced orbital TIG welding with internal and external argon shielding produces uniform, defect-free welds with minimal heat-affected zone (HAZ), eliminating leakage risks and maintaining the full corrosion resistance of the base material throughout the weld joint.
4. Customizable Design for GSN Heat Exchanger Integration: Flexible configuration options including variable coil diameter, pitch, tube dimensions, and end treatments allow seamless integration into diverse GSN heat exchanger shell designs, accommodating refrigerant capacities from 3 kW to 500 kW.
5. Full Traceability and Documentation: Each production batch is fully traceable from raw material mill certificates through all manufacturing stages to final product testing, providing complete quality assurance documentation for regulatory compliance and customer verification.